This proposal seeks to elucidate the structure and function of a variety of iron-containing enzymes involved in oxygen activation and acetate synthesis. Moreover, it is proposed to investigate the electronic structure of synthetic complexes that mimic structural and electronic features of the enzymes under study. The experimental techniques employed are 57Fe Mossbauer spectroscopy, Electron Paramagnetic Resonance and SQUID magnetometry. (1) Studies of the diiron proteins methane monooxygenase, ribonucleotide reductase, delta9 desaturase, toluene monooxygenase, phenol hydroxylase and alkane hydroxylase will be continued with particular focus on characterizing the electronic structure of catalytic intermediates. (2) This research will be complemented by studies of model complexes to gain insight into the electronic structure of the active sites of the enzymes. (3) Studies of FNR transcription factor as isolated and in whole E.coli cells will be continued. (4) Mossbauer studies of 1-aminopropane-1-carboxylate oxidase from avocado, cloned into E. coli, will be performed. (5) The Collins laboratory at Carnegie Mellon University has designed a variety of iron-containing complexes that are potent catalysts for dye and pulp bleaching, and that have high promise in green chemistry. The high- valent states of these complexes will be investigated with the goal of characterizing their catalytic behavior. These complexes are also of interest as spectroscopic benchmarks for FeIV states in proteins. (6) Experimental and theoretical studies of the structure the Nickel- [4Fe-4S] cluster assemblies of carbon monoxide dehydrogenases isolated from Clostridium thermoaceticum and Rhodospirillum rubrum will be continued. These studies will be extended to iron-hydrogenases which appear to have a cluster assembly involving a[4Fe4S] cluster as well.